<?xml version="1.0" encoding="UTF-8"?><edgarSubmission xmlns="http://www.sec.gov/edgar/ownership" xmlns:com="http://www.sec.gov/edgar/common">
  <headerData>
    <submissionType>144</submissionType>
    <filerInfo>
      <filer>
        <filerCredentials>
          <cik>0001991125</cik>
          <ccc>XXXXXXXX</ccc>
        </filerCredentials>
      </filer>
      <liveTestFlag>LIVE</liveTestFlag>



    </filerInfo>
  </headerData>
  <formData>
    <issuerInfo>
      <issuerCik>0001835830</issuerCik>
      <issuerName>Klaviyo, Inc.</issuerName>
      <secFileNumber>001-41806</secFileNumber>
      <issuerAddress>
        <com:street1>125 SUMMER STREET, FLOOR 6</com:street1>
        <com:city>BOSTON</com:city>
        <com:stateOrCountry>MA</com:stateOrCountry>
        <com:zipCode>02110</com:zipCode>
      </issuerAddress>
      <issuerContactPhone>800-338-1744</issuerContactPhone>
      <nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>Hallen Ed</nameOfPersonForWhoseAccountTheSecuritiesAreToBeSold>
      <relationshipsToIssuer>
        <relationshipToIssuer>Officer</relationshipToIssuer>
        <relationshipToIssuer>Director</relationshipToIssuer>
      </relationshipsToIssuer>
    </issuerInfo>
    <securitiesInformation>
      <securitiesClassTitle>Series A</securitiesClassTitle>
      <brokerOrMarketmakerDetails>
        <name>Fidelity Brokerage Services LLC</name>
        <address>
          <com:street1>900 Salem Street</com:street1>
          <com:city>Smithfield</com:city>
          <com:stateOrCountry>RI</com:stateOrCountry>
          <com:zipCode>02917</com:zipCode>
        </address>
      </brokerOrMarketmakerDetails>
      <noOfUnitsSold>757</noOfUnitsSold>
      <aggregateMarketValue>22822.56</aggregateMarketValue>
      <noOfUnitsOutstanding>137856147</noOfUnitsOutstanding>
      <approxSaleDate>12/15/2025</approxSaleDate>
      <securitiesExchangeName>NYSE</securitiesExchangeName>
    </securitiesInformation>
    <securitiesToBeSold>
      <securitiesClassTitle>Series A</securitiesClassTitle>
      <acquiredDate>09/25/2012</acquiredDate>
      <natureOfAcquisitionTransaction>Founders Shares</natureOfAcquisitionTransaction>
      <nameOfPersonfromWhomAcquired>Issuer</nameOfPersonfromWhomAcquired>
      <isGiftTransaction>N</isGiftTransaction>
      <amountOfSecuritiesAcquired>757</amountOfSecuritiesAcquired>
      <paymentDate>09/25/2012</paymentDate>
      <natureOfPayment>Compensation</natureOfPayment>
    </securitiesToBeSold>
    <nothingToReportFlagOnSecuritiesSoldInPast3Months>N</nothingToReportFlagOnSecuritiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>Hodgkins Trust</name>
        <address>
          <com:street1>125 Summer Street</com:street1>
          <com:street2>6th Floor</com:street2>
          <com:city>Boston</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02110</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>Series A</securitiesClassTitle>
      <saleDate>09/15/2025</saleDate>
      <amountOfSecuritiesSold>22224</amountOfSecuritiesSold>
      <grossProceeds>703493.05</grossProceeds>
    </securitiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>Hodgkins Llc</name>
        <address>
          <com:street1>125 Summer Street</com:street1>
          <com:street2>6th Floor</com:street2>
          <com:city>Boston</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02110</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>Series A</securitiesClassTitle>
      <saleDate>09/15/2025</saleDate>
      <amountOfSecuritiesSold>67524</amountOfSecuritiesSold>
      <grossProceeds>2142377.45</grossProceeds>
    </securitiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>Hodgkins Trust</name>
        <address>
          <com:street1>125 Summer Street</com:street1>
          <com:street2>6th Floor</com:street2>
          <com:city>Boston</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02110</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>Series A</securitiesClassTitle>
      <saleDate>11/10/2025</saleDate>
      <amountOfSecuritiesSold>8572</amountOfSecuritiesSold>
      <grossProceeds>257604.18</grossProceeds>
    </securitiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>Hodgkins Llc</name>
        <address>
          <com:street1>125 Summer Street</com:street1>
          <com:street2>6th Floor</com:street2>
          <com:city>Boston</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02110</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>Series A</securitiesClassTitle>
      <saleDate>11/10/2025</saleDate>
      <amountOfSecuritiesSold>50920</amountOfSecuritiesSold>
      <grossProceeds>1529816.71</grossProceeds>
    </securitiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>Hodgkins Trust</name>
        <address>
          <com:street1>125 Summer Street</com:street1>
          <com:street2>6th Floor</com:street2>
          <com:city>Boston</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02110</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>Series A</securitiesClassTitle>
      <saleDate>11/11/2025</saleDate>
      <amountOfSecuritiesSold>545</amountOfSecuritiesSold>
      <grossProceeds>16350.54</grossProceeds>
    </securitiesSoldInPast3Months>
    <securitiesSoldInPast3Months>
      <sellerDetails>
        <name>Hodgkins Llc</name>
        <address>
          <com:street1>125 Summer Street</com:street1>
          <com:street2>6th Floor</com:street2>
          <com:city>Boston</com:city>
          <com:stateOrCountry>MA</com:stateOrCountry>
          <com:zipCode>02110</com:zipCode>
        </address>
      </sellerDetails>
      <securitiesClassTitle>Series A</securitiesClassTitle>
      <saleDate>11/11/2025</saleDate>
      <amountOfSecuritiesSold>2266</amountOfSecuritiesSold>
      <grossProceeds>67981.00</grossProceeds>
    </securitiesSoldInPast3Months>
    <remarks>Today's sale includes 600 shares sold from Hodgkins Llc (of which Edward W Hallen is an authorized individual and account stake order) and 157 shares sold from Hodgkins Trust (of which Edward W Hallen is an account stakeholder). Sales from the past 3 months also occurred in these accounts.</remarks>
    <noticeSignature>
      <noticeDate>12/15/2025</noticeDate>
      <planAdoptionDates>
        <planAdoptionDate>06/12/2025</planAdoptionDate>
      </planAdoptionDates>
      <signature>/s/ Daniel Tucci, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Edward Hallen</signature>
    </noticeSignature>
  </formData>
</edgarSubmission>
